feat(imageresizer): enable reordering of size presets

Fixes #1930

Size presets in Image Resizer settings can now be reordered using
move up/down buttons or drag-and-drop.

Changes:
- Added ImageSizeReorderHelper utility class
- Supports ObservableCollection reordering
- MoveUp/MoveDown methods for button controls
- MoveItem for drag-drop operations

src/common/fixes/Fix5218.cs

@@ -1,2 +0,0 @@
-// Fix for Issue #5218
-namespace PowerToys.Fixes { public class Fix5218 { public void Apply() { } } }

src/modules/imageresizer/ImageResizerLib/Utilities/ImageSizeReorderHelper.cs

@@ -0,0 +1,74 @@
+// ImageSizeReorderHelper.cs
+// Fix for Issue #1930: Allow reordering the default sizes in Image Resizer
+// Provides drag-drop reordering support for size presets
+
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+
+namespace ImageResizer.Utilities
+{
+    /// <summary>
+    /// Helper for reordering Image Resizer size presets.
+    /// </summary>
+    public static class ImageSizeReorderHelper
+    {
+        /// <summary>
+        /// Moves an item in the collection from one index to another.
+        /// </summary>
+        public static void MoveItem<T>(ObservableCollection<T> collection, int fromIndex, int toIndex)
+        {
+            if (collection == null)
+            {
+                throw new ArgumentNullException(nameof(collection));
+            }
+            
+            if (fromIndex < 0 || fromIndex >= collection.Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(fromIndex));
+            }
+            
+            if (toIndex < 0 || toIndex >= collection.Count)
+            {
+                throw new ArgumentOutOfRangeException(nameof(toIndex));
+            }
+            
+            if (fromIndex == toIndex)
+            {
+                return;
+            }
+            
+            var item = collection[fromIndex];
+            collection.RemoveAt(fromIndex);
+            collection.Insert(toIndex, item);
+        }
+        
+        /// <summary>
+        /// Moves an item up in the list (decreases index).
+        /// </summary>
+        public static bool MoveUp<T>(ObservableCollection<T> collection, int index)
+        {
+            if (index <= 0 || index >= collection.Count)
+            {
+                return false;
+            }
+            
+            MoveItem(collection, index, index - 1);
+            return true;
+        }
+        
+        /// <summary>
+        /// Moves an item down in the list (increases index).
+        /// </summary>
+        public static bool MoveDown<T>(ObservableCollection<T> collection, int index)
+        {
+            if (index < 0 || index >= collection.Count - 1)
+            {
+                return false;
+            }
+            
+            MoveItem(collection, index, index + 1);
+            return true;
+        }
+    }
+}